JP2018040253A - Internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively inhibit occurrence of knocking by a simple structure without an increase in weight of a piston.SOLUTION: An engine 1 includes: a cylinder block 3 formed with a cylinder bore 2; a cylinder head 4 connected to one end face in a cylinder axial direction of the cylinder block 3; and a piston 20 provided so as to be reciprocable in the cylinder bore 2 and defining a combustion chamber 6 between the cylinder head 4 and the piston. A combustion chamber expansion part 50 for expanding the combustion chamber 6 to an outer side in a radial direction is formed on at least one of the cylinder block 3 and the cylinder head 4.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to an internal combustion engine.

  In a spark ignition type internal combustion engine in which a piston is reciprocated in a cylinder formed in a cylinder block and a combustion chamber is defined between a cylinder head and a piston disposed on the upper surface of the cylinder block, compression is performed in the combustion chamber. When the mixed gas mixture is ignited by the spark discharge of the spark plug, a flame nucleus is generated, and the flame is transmitted through the combustion chamber from the flame nucleus.

  On the other hand, since the temperature of the air-fuel mixture rises due to compression in the compression stroke or compression of the combustion gas, self-ignition (knocking) occurs before the flame of the unburned air-fuel mixture (end gas) located far from the spark plug reaches the flame. There is a case. In order to suppress the occurrence of knocking, it is necessary to complete flame propagation as soon as possible before the end gas self-ignites. Currently, in order to suppress self-ignition, measures such as retarding control of the ignition timing, which is accompanied by a decrease in thermal efficiency, are taken.

  Moreover, as an internal combustion engine that can suppress the occurrence of knocking with a simple structure, a combustion chamber is formed in parallel with the top surface of the piston from the two inclined surfaces formed in the cylinder head and the lower edges of the inclined surfaces. The present applicant has proposed an internal combustion engine that has two squish portions and is provided with an elongated recess extending in an arc shape in the circumferential direction of the piston at one or two of the peripheral portions of the piston top surface. . In this internal combustion engine, when the piston reaches the top dead center, a squish that flows from the peripheral edge of the combustion chamber toward the center side is generated. Generation | occurrence | production of knocking is suppressed by acting so that it may raise. The occurrence of knocking is also suppressed by improving the cooling performance by increasing the area of the piston surface exposed to the flame by the depth of the recess.

Japanese Patent Laid-Open No. 2006-89651

  However, the internal combustion engine described in Patent Document 1 has a structure in which a concave portion is provided on the top land above the top ring from the top surface of the piston, rather than a structure corresponding to the depth of the concave portion on the top portion of the piston. Close to the added structure. As a result, the weight of the piston increases and the swinging motion of the piston becomes intense due to an increase in the center of gravity of the piston. When the head swings violently, deterioration of fuel consumption and vibration due to increased friction become problems. Further, while the surface area of the piston increases, the heat absorbed by the increased area is released to the cooling water from the water jacket formed in the cylinder block, and the heat transfer path is long. Therefore, the improvement in cooling performance is limited, and there is room for further improvement in the suppression of knocking.

  Furthermore, the squish provided for suppressing the occurrence of knocking does not perform the function of generating the squish in the portion where the recess is provided. In addition, the internal combustion engine described in Patent Document 1 has room for improvement in reducing harmful exhaust gas components such as hydrocarbons. That is, normally, fuel and lubricating oil enter the ring clevis between the top land and the cylinder during the compression stroke. The flame ignited when the piston is near the top dead center cannot enter the ring clevis, and unburned fuel or the like remains in the ring clevis after the combustion is completed. Harmful substances such as hydrocarbons contained in the unburned fuel remaining in the ring clevis evaporate as the piston continues to descend after completion of combustion, and are mixed with the burned gas and discharged outside as exhaust gas. In the internal combustion engine described in Patent Document 1, the top ring is provided below the top surface of the piston by the depth of the recess, and the position of the top land is shifted downward, so that the discharge of unburned fuel cannot be improved.

  In view of such a background, it is an object of the present invention to provide an internal combustion engine that can effectively suppress the occurrence of knocking without increasing the weight of a piston and with a simple structure.

  In order to solve such problems, an internal combustion engine (1) according to an embodiment of the present invention includes a cylinder block (3) in which a cylinder bore (2) is formed, and a cylinder axis (A) direction of the cylinder block. A cylinder head (4) coupled to one end surface of the cylinder, and a piston (20) provided in a reciprocating manner in the cylinder bore and defining a combustion chamber (6) between the cylinder head and the cylinder head, At least one of the block and the cylinder head is formed with a combustion chamber expansion portion (50) for expanding the combustion chamber radially outward when the piston is at top dead center.

  According to this configuration, since the combustion chamber expansion portion is formed in at least one of the cylinder block and the cylinder head, it is not necessary to increase the piston weight. In addition, since the concave portion, that is, the area increasing portion of the surface of the combustion chamber exposed to the flame is formed not in the piston but in at least one of the cylinder block and the cylinder head, the heat transfer path from the portion is short. Therefore, cooling performance is improved and self-ignition at the peripheral edge of the combustion chamber is suppressed. For these reasons, the occurrence of knocking is effectively suppressed.

  Further, a pressure gradient is generated in the combustion chamber in the early stage of combustion, and the air-fuel mixture rapidly moves from the central portion of the combustion chamber toward the peripheral combustion chamber expansion portion. This air-fuel mixture passes through the gap between the peripheral edge of the piston near the top dead center and the peripheral edge of the combustion chamber of the cylinder head and flows into the expansion chamber expansion section, thereby generating a strong turbulent flow in the expansion chamber expansion section. . Occurrence of knocking is also suppressed by suppressing the self-ignition at the peripheral portion of the combustion chamber by cooling the periphery of the combustion chamber expansion portion by this turbulent flow.

  Another embodiment of the present invention is characterized in that, in the above configuration, the combustion chamber expansion portion is formed so as to open at least to the one end surface of the cylinder block.

  According to this structure, the process for forming a combustion chamber expansion part in a cylinder block is easy.

  According to another embodiment of the present invention, in the above-described configuration, when the piston (20) is at the top dead center, the combustion chamber expansion portion (50) is arranged so that the piston top ring (from the one end surface of the cylinder block) 35) is formed in the cylinder block (3) with a depth (D) that does not reach 35).

  According to this configuration, the fuel that has entered the ring clevis between the top land of the piston and the cylinder block is mixed with the air-fuel mixture by the turbulent flow generated in the combustion chamber expansion, and propagates from the center side portion of the combustion chamber To burn. Therefore, harmful substances such as hydrocarbons contained in the exhaust gas are reduced.

  According to another embodiment of the present invention, in the above configuration, the combustion chamber (6) has a squish portion (45) that is a gap that causes squish when the piston reaches top dead center. The cylinder head (4) and the top surface (27) of the piston (20) extending in parallel to each other are formed, and the combustion chamber expansion portion (50) is provided radially outside the squish portion. It is characterized by being.

  According to this configuration, the entire squish part functions to generate squish and to stir the air-fuel mixture, and the flame propagation speed is increased. In addition, the air-fuel mixture that moves rapidly from the central part of the combustion chamber toward the peripheral part at the beginning of combustion passes through the squish part and flows into the combustion chamber expansion part, generating strong turbulence in the combustion chamber expansion part. Let Thereby, the peripheral part of a combustion chamber expansion part is cooled effectively, and the self-ignition in a combustion chamber peripheral part is suppressed further. For these reasons, the occurrence of knocking is further suppressed.

  Another embodiment of the present invention is characterized in that, in the above configuration, the combustion chamber expansion portion (50) is formed at least on the intake side of the combustion chamber (6). Here, the intake side means the side on which the intake port is formed.

  The exhaust side of the combustion chamber (the side where the exhaust port is formed) becomes a higher temperature than the intake side because it becomes a passage path for the burned gas that has become hot. Since the cylinder block and the meat part of the cylinder head absorb this heat, if the combustion chamber expansion is formed on the exhaust side, knocking may easily occur depending on the different heat conditions depending on the specifications of the internal combustion engine. . According to this configuration, since at least the combustion chamber expansion portion is provided on the intake side where there is no problem of occurrence of knocking due to thermal conditions, knocking is reliably suppressed.

  In another embodiment of the present invention, in the above-described configuration, the combustion chamber expansion portion (50) is provided only on the intake side of the combustion chamber (6), or on only two locations on the intake side and the exhaust side of the combustion chamber. It is formed.

  According to this configuration, it is not necessary to form the combustion chamber expansion portion on the piston pin axial direction side of the combustion chamber in which knocking is unlikely to occur, and the processing amount and processing time for forming the combustion chamber expansion portion can be reduced. it can. Moreover, it can suppress that the dimension of the piston pin axial direction (crankshaft direction) of an internal combustion engine increases for formation of a combustion chamber expansion part.

  According to another embodiment of the present invention, in the above configuration, the combustion chamber expansion portion (50) extends in a circumferential direction of the cylinder bore (2), and a sectional area of the piston (20) toward the piston pin axial direction. Is formed to be small.

  According to this configuration, it is possible to reduce the amount of processing for forming the combustion chamber expansion portion in a portion near the piston pin axial direction of the combustion chamber where knocking hardly occurs. It is possible to suppress an increase in the dimension of the internal combustion engine in the piston pin axial direction (crank shaft direction) due to the formation of the combustion chamber expansion portion.

  According to another embodiment of the present invention, in the above-described configuration, the combustion chamber expansion portion (50) extends from the one end surface of the cylinder block (3) to the other end in a cross section along the radial direction of the cylinder bore (2). It has a shape that the width in the radial direction becomes smaller.

  According to this configuration, since a strong turbulent flow is generated in the combustion chamber expansion portion as compared with the case where the combustion chamber expansion portion has a rectangular cross-sectional shape, the occurrence of knocking is more effectively suppressed.

  Another embodiment of the present invention is characterized in that, in the above configuration, the radially outer contour of the combustion chamber expansion portion (50) has a waveform when viewed in the direction of the cylinder axis (A).

  According to this configuration, not only a flow along the radial direction of the piston and a flow along the circumferential direction of the piston are generated in the air-fuel mixture in the expansion portion of the combustion chamber, but also a swirl flow in each wave shape portion is generated. Thereby, mixing of unburned fuel in the combustion chamber expansion part and cooling around the combustion chamber expansion part are promoted, and the occurrence of knocking is suppressed.

  Thus, according to the present invention, it is possible to provide an internal combustion engine that can effectively suppress the occurrence of knocking with a simple structure without increasing the piston weight.

Side sectional view which shows the principal part of the engine which concerns on embodiment Side sectional view of the piston shown in FIG. FIG. 1 is a schematic plan view showing the essential part of the internal combustion engine seen through along line III-III in FIG. Operational explanatory diagram of the engine shown in FIG. Main part schematic plan view of the engine showing a modification of the combustion chamber expansion part Cross-sectional view of the main part of the engine showing a modification of the combustion chamber expansion part

  Hereinafter, an embodiment in which the present invention is applied to a four-valve gasoline direct injection engine will be described in detail with reference to the drawings.

  FIG. 1 is a side sectional view showing a main part of an engine 1 according to the embodiment. As shown in FIG. 1, the engine 1 includes a cylinder block 3 in which a cylinder bore 2 (cylinder) is formed, and a cylinder head 4 coupled to an upper surface that is one end surface of the cylinder block 3 in the cylinder axial direction. ing. In the present embodiment, a plurality of cylinder bores 2 are arranged in a row on the cylinder block 3. With the cylinder bore 2 as a reference, the cylinder axis A direction is defined as the up-down direction and the cylinder row direction is defined as the left-right direction. A water jacket 5 for cooling is formed in the cylinder block 3 so as to surround the cylinder bore 2.

  On the lower end surface of the cylinder head 4, two inclined surfaces 4 a and 4 b are formed that define an upper part of a pent roof type combustion chamber 6 that is continuous with the cylinder bore 2. The two inclined surfaces 4a and 4b extend in the cylinder row direction, two intake ports 7 are opened on one inclined surface 4a, and two exhaust ports 8 are opened on the other inclined surface 4b. Yes. The intake port 7 and the exhaust port 8 are opened and closed by an intake valve and an exhaust valve, respectively, which are poppet valves. In the combustion chamber 6, the side on which the two intake ports 7 orthogonal to the vertical direction and the left-right direction are arranged is the intake side, and the side on which the two exhaust ports 8 are arranged is the exhaust side. Two parallel surfaces 4c and 4d are formed on the outer sides of the two inclined surfaces 4a and 4b so as to extend from the respective lower edges to the intake side and the exhaust side in parallel with the upper surface of the cylinder block 3.

  A spark plug hole 11 penetrating to the upper surface of the cylinder head 4 is formed at the center of the portion defining the combustion chamber 6 of the cylinder head 4, and a spark plug 12 is inserted into the spark plug hole 11. . The spark plug 12 is arranged so that a ground electrode 13 provided at the tip thereof protrudes from the spark plug hole 11 into the combustion chamber 6. An injection nozzle hole 14 penetrating to the side surface of the cylinder head 4 is formed in the intake side portion of the combustion chamber 6 and between the two intake ports 7. A fuel injection nozzle 15 is inserted into the injection nozzle hole 14. Also in the cylinder head 4, a water jacket 16 for cooling covers the combustion chamber 6 and surrounds the exhaust port 8 and the like.

  A piston 20 is disposed in the cylinder bore 2 so as to be able to reciprocate up and down. Piston 20 defines combustion chamber 6 between cylinder head 4 (inclined surfaces 4a, 4b, parallel surfaces 4c, 4d, etc.). The piston 20 has a bilaterally symmetric shape, and a pair of skirts projecting downward from a disk-shaped piston head portion 21 (crown portion) and an intake side portion and an exhaust side portion of a peripheral portion of the piston head portion 21. Part 22 and a pair of sidewalls 23 that connect corresponding side edges of each skirt part 22 to each other. The outer diameters of the piston top portion 21 and the pair of skirt portions 22 are slightly smaller than the inner diameter of the cylinder bore 2.

  FIG. 2 is a side sectional view of the piston 20 shown in FIG. As shown in FIGS. 1 and 2, the piston top 21 is a disc-shaped top plate 25, and a cylinder that protrudes downward from the periphery of the top plate 25 and extends along the periphery. Wall 26. A surface facing upward of the top plate 25 is referred to as a top surface 27, and a surface facing downward or inward of the piston top 21 is referred to as a back surface 28. A first annular groove 31, a second annular groove 32, and a third annular groove 33 extending in the circumferential direction are formed in order from the top on the outer peripheral surfaces of the top plate 25 and the cylindrical wall 26. A plurality of oil holes 34 communicating the bottom surface of the third annular groove 33 and the back surface 28 of the cylindrical wall 26 are formed in each of the intake side portion and the exhaust side portion of the third annular groove 33.

  The first annular groove 31 and the second annular groove 32 have a top ring 35 and a second ring 36 (see FIG. 1) made of a compression ring, and the third annular groove 33 has an oil ring 37 (FIG. 1), respectively. It fits so that it may protrude from the outer peripheral surface of the top part 21. The upper portion of the top ring 35 on the outer peripheral surface of the piston top 21 is a top land 38 (FIG. 2), and there is a gap between the top land 38 and the cylinder block 3 (the inner peripheral surface forming the cylinder bore 2). A ring clevis 39 (FIG. 1) is formed.

  Each skirt portion 22 protrudes downward from the intake side portion and the exhaust side portion of the cylindrical wall 26. Each skirt portion 22 extends in the circumferential direction along the lower end of the cylindrical wall 26, and the outer surface thereof is an arc surface continuous to the outer peripheral surface of the cylindrical wall 26.

  Each side wall 23 protrudes downward from the back surface 28 of the cylindrical wall 26. Each side wall 23 is formed with a piston pin boss 40 that is coaxial with each other. Each piston pin boss 40 is inserted with a piston pin (not shown) that rotatably connects the piston 20 to a piston rod (not shown).

  An annular flat surface portion 41 made of a plane orthogonal to the cylinder axis A is formed on the peripheral edge portion of the top surface 27 of the piston 20. On the inner side of the annular flat surface portion 41, a protruding portion 42 that protrudes upward with respect to the annular flat surface portion 41 in a portion extending from the central portion (cylinder axis A side) to the exhaust side, and an annular flat surface portion 41 in the intake side portion A recessed portion 43 that is recessed is formed. An intake valve recess (not shown) for avoiding interference with the intake valve is provided in the left and right sides of the recessed portion 43, respectively. Exhaust valve recesses (not shown) for avoiding interference with the exhaust valves are respectively provided on the left and right sides of the protrusions 42. An exhaust-side convex portion 44 that protrudes in parallel with the inclined surface 4 b on the exhaust side of the cylinder head 4 is formed on the outer peripheral side portion between the two exhaust valve recesses in the protruding portion 42.

  FIG. 1 shows the engine 1 with the piston 20 at top dead center. In this state, the annular flat surface portion 41 of the piston 20 substantially coincides with the upper surface of the cylinder block 3 and is positioned slightly below the two parallel surfaces 4 c and 4 d of the cylinder head 4. Due to the small gap between the parallel surfaces 4c and 4d of the cylinder head 4 and the top surface 27 of the piston 20, the mixing in the direction perpendicular to the cylinder axis A when the piston 20 reaches top dead center. A squish portion 45 is formed for generating a squish that is a flow of air.

  FIG. 3 is a schematic plan view showing the essential part of the engine 1 through the line III-III in FIG. As shown in FIGS. 1 to 3, the exhaust-side convex portion 44 extends in parallel with the inclined surface 4 b of the cylinder head 4, whereby the exhaust-side parallel surface 4 d of the cylinder head 4 and the top surface of the piston 20. 27 is enlarged to the center side of the combustion chamber 6.

  As shown in FIG. 1, the inner peripheral surface defining the cylinder bore 2 of the cylinder block 3 is recessed so as to extend in the circumferential direction of the cylinder bore 2 at the upper end of the cylinder bore 2, and the combustion chamber 6 is formed in the radial direction. A combustion chamber expansion portion 50 that extends outward is formed. The combustion chamber expansion portion 50 has a fan-shaped cross-sectional shape that opens to the inner peripheral surface and the upper surface of the cylinder block 3. That is, the combustion chamber expansion portion 50 is formed by a concave portion having an arcuate cross-sectional shape in which the width in the radial direction of the cylinder bore 2 decreases from the upper end to the lower end of the cylinder block 3.

  As shown in FIG. 3, in this embodiment, the combustion chamber expansion portion 50 is formed in an arc shape at two locations on the intake side and the exhaust side of the cylinder bore 2. Each of the combustion chamber expansion portions 50 is formed so that the cross-sectional area gradually decreases toward both ends in the left-right direction, in other words, the cross-sectional area decreases toward the piston pin axial direction side of the piston 20. The cross section of the combustion chamber extension 50 is the largest in the cross section of FIG. 1 that passes through the cylinder axis A and is orthogonal to the cylinder row direction. In this cross section, the combustion chamber extension 50 is formed such that the depth D from the upper surface of the cylinder block 3 does not reach the top ring 35 of the piston 20 when the piston 20 shown in FIG. ing.

  As shown in FIG. 3, the combustion chamber expansion portion 50 is formed longer than the circumferential length of the adjacent squish portion 45 on both the intake side and the exhaust side, and is squished outwardly in the radial direction of the squish portion 45. It is provided over a predetermined angle range that surrounds the entire portion 45.

  Next, the operation and effect of the engine 1 configured as described above will be described.

  4A is a side cross-sectional view of the main part of the engine 1 when the piston 20 is at the top dead center as in FIG. 1, and FIG. 4B is a diagram illustrating the combustion of the air-fuel mixture completed in the downward stroke. It is principal part side sectional drawing of the engine 1 at the time. When the piston 20 ascends during the compression stroke, the lubricating oil adhering to the inner peripheral surface of the cylinder block 3 or the fuel injected from the fuel injection nozzle 15 is swept up by the top ring 35 and the ring clevis 39 (FIG. 4). (See (B)). As shown in FIG. 4A, when the piston 20 reaches the top dead center through the compression stroke, the squish portion 45 generates squish. At this time, since the combustion chamber expansion portion 50 has an extremely small volume compared to the portion on the center side of the squish portion 45 of the combustion chamber 6, the squish mainly flows from the peripheral portion of the combustion chamber 6 toward the center side. Stir the mixture to generate turbulence.

  When the air-fuel mixture is ignited by the spark plug 12 in such a state, the flame spreads from the center side of the combustion chamber 6 toward the peripheral portion at a relatively high propagation speed. Combustion of the air-fuel mixture by flame propagation is completed by the time the piston 20 is lowered to the position shown in FIG. At this time, a pressure gradient is generated in the combustion chamber 6 at the early stage of combustion, and the air-fuel mixture rapidly moves from the central portion of the combustion chamber 6 toward the combustion chamber expansion portion 50 at the peripheral portion. This air-fuel mixture is formed between the peripheral portion of the piston 20 and the cylinder in the gap of the squish portion 45 formed in the peripheral portion of the piston 20 near the top dead center shown in FIG. By passing through the gap with the head 4 and flowing into the combustion chamber expansion portion 50, a strong turbulent flow is generated in the combustion chamber expansion portion 50. Thereby, the periphery of the combustion chamber expansion portion 50 is cooled, and self-ignition at the peripheral portion of the combustion chamber 6 is suppressed.

  As described above, the combustion chamber expansion portion 50 that expands the combustion chamber 6 radially outward is formed in the cylinder block 3, so that self-ignition at the peripheral portion of the combustion chamber 6 is suppressed and occurrence of knocking is suppressed. The Moreover, since the combustion chamber expansion part 50 is formed not in the piston 20 but in the cylinder block 3, it is not necessary to add a meat part to the piston top part 21 of the piston 20, and it is not necessary to increase the piston weight. In addition, a combustion chamber expansion portion 50 that is a surface area increasing portion of the combustion chamber 6 exposed to the flame is formed in the cylinder block 3 instead of the piston 20. Therefore, as shown in FIG. 1, the heat transfer path from the portion defining the combustion chamber expansion portion 50 to the water jacket 5 is shortened and the cooling performance is improved. Self-ignition is suppressed.

  Further, since the combustion chamber expansion portion 50 is formed so as to open on the upper surface of the cylinder block 3, processing for forming the combustion chamber expansion portion 50 is easy.

  Further, the combustion chamber extension 50 is formed in the cylinder block 3 with a depth D that does not reach the top ring 35 of the piston 20 from the upper surface of the cylinder block 3 when the piston 20 is at the top dead center. Therefore, the fuel that has entered the ring clevis 39 between the top land 38 of the piston 20 and the cylinder block 3 is mixed into the air-fuel mixture by the turbulent flow generated in the combustion chamber expansion portion 50 and propagates from the central side portion of the combustion chamber 6. Burns with a flame. Therefore, harmful substances such as hydrocarbons contained in the exhaust gas are reduced.

  In the present embodiment, the combustion chamber 6 has a squish part 45 that is a gap that causes squish when the piston 20 reaches top dead center, and the squish part 45 has a lower surface of the cylinder head 4 that extends parallel to each other. The combustion chamber expansion part 50 is provided on the radially outer side of the squish part 45. Therefore, as described with reference to FIG. 4A, the entire squish unit 45 functions to generate squish and to stir the air-fuel mixture, thereby increasing the flame propagation speed. In addition, the air-fuel mixture that moves rapidly from the center side portion of the combustion chamber 6 toward the peripheral portion in the early stage of combustion passes through the squish portion 45 and flows into the combustion chamber expansion portion 50, thereby being stronger in the combustion chamber expansion portion 50. Generate turbulence. Thereby, the peripheral part of the combustion chamber expansion part 50 is cooled effectively, and the self-ignition around the expansion part of the combustion chamber 6 is further suppressed. For these reasons, the occurrence of knocking is further suppressed.

  As shown in FIG. 3, in this embodiment, the combustion chamber expansion portion 50 is formed only at two locations on the intake side and the exhaust side of the combustion chamber 6. Therefore, it is not necessary to form the combustion chamber expansion portion 50 on the cylinder row direction side of the combustion chamber 6 where knocking is unlikely to occur, and the processing amount and processing time for forming the combustion chamber expansion portion 50 can be reduced. In addition, an increase in the dimension of the engine 1 in the cylinder row direction due to the formation of the combustion chamber expansion portion 50 can be suppressed.

  In this embodiment, as shown in FIG. 3, the combustion chamber expansion portion 50 is formed on both the intake side and the exhaust side of the combustion chamber 6, but may be formed only on the intake side. The exhaust side of the combustion chamber 6 is likely to be hotter than the intake side because it becomes a passage path for the burned gas that has become hot, but if the combustion chamber expansion portion 50 is formed only on the intake side, the cylinder block 3 and the meat part of the cylinder head 4 (the part where the combustion chamber expansion part 50 is not formed) absorbs heat. In other words, when the combustion chamber expansion portion 50 is formed on the exhaust side, knocking may be likely to occur depending on different thermal conditions depending on the specifications of the engine 1, but only on the intake side where there is no problem of knocking due to thermal conditions. By providing the combustion chamber expansion portion 50 in the knocking, knocking can be reliably suppressed.

  The combustion chamber extending portion 50 extends in the circumferential direction of the cylinder bore 2 and is formed so that the cross-sectional area becomes smaller toward the cylinder row direction side of the piston 20. Therefore, it is possible to reduce the amount of processing for forming the combustion chamber expansion portion 50 in the portion of the combustion chamber 6 that is unlikely to cause knocking in the piston pin axial direction. Moreover, it can suppress that the dimension of the cylinder row direction of the engine 1 increases for formation of the combustion chamber expansion part 50. FIG.

  As shown in FIG. 1, the combustion chamber expansion portion 50 has a shape in which the radial width decreases from the upper end to the lower end of the cylinder block 3 in a cross section along the radial direction of the cylinder bore 2. Therefore, compared with the case where the combustion chamber expansion portion 50 has a rectangular cross-sectional shape (see FIG. 5A), a strong turbulent flow is generated in the combustion chamber expansion portion 50, and the occurrence of knocking is more effectively suppressed.

  Note that the cross-sectional shape of the combustion chamber expansion portion 50 is not limited to the arc shape as described above. FIGS. 5A to 5C are side cross-sectional views of the main part of the engine 1 showing modifications of the combustion chamber expansion portion 50, respectively. For example, as shown in FIG. 5A, the combustion chamber extension 50 may have a rectangular cross-sectional shape. Alternatively, as shown in FIG. 5B, the cylinder block 3 may be formed not only in a sector fan shape but also in the cylinder head 4 so as to be continuous in a sector fan shape. Further, as shown in FIG. 5C, the combustion chamber expansion portion 50 may be formed in the cylinder block 3 with a rectangular cross section, and the cylinder head 4 may be formed in a sector fan shape.

  Further, although not shown, the combustion chamber expansion portion 50 may be formed only on the cylinder head 4. However, in this case, it is difficult to mix the fuel that has entered the ring clevis 39 into the air-fuel mixture due to the turbulent flow generated in the combustion chamber expansion portion 50. Therefore, the combustion chamber extension 50 is preferably formed in the cylinder block 3.

  FIGS. 6A and 6B are schematic plan views of main parts of the engine 1 corresponding to FIG. 3, each showing a modification of the combustion chamber expansion portion 50. The combustion chamber expansion portion 50 may be formed in an annular shape around the entire circumference of the combustion chamber 6 as shown in FIG. In this case, the cross-sectional shape of the combustion chamber expansion portion 50 may be constant or may be changed so as to become smaller toward the cylinder row direction side.

  Alternatively, as shown in FIG. 6B, the radially outer contour of the combustion chamber expansion portion 50 may have a waveform. In the illustrated example, the radially outer contour of the combustion chamber expansion portion 50 has a waveform only on the intake side of the combustion chamber 6. In another example, the waveform may be only on the exhaust side of the combustion chamber 6 or on both the intake side and the exhaust side. As described above, the contour of the radially outer side of the combustion chamber expansion portion 50 is corrugated, so that the air-fuel mixture of the combustion chamber expansion portion 50 has a flow along the radial direction of the piston 20 and a flow along the circumferential direction of the piston 20. Not only does this occur, but a swirling flow in each corrugated part also occurs. Thereby, mixing of unburned fuel in the combustion chamber expansion portion 50 and cooling around the combustion chamber expansion portion 50 are promoted, and the occurrence of knocking is suppressed.

  Although the description of the specific embodiment is finished as described above, the present invention is not limited to the above embodiment and can be widely modified. For example, in the above embodiment, the pent roof type combustion chamber 6 is formed in the engine 1, but the combustion chamber 6 may have other shapes. In addition, the specific configuration, arrangement, quantity, angle, and the like of each member and part can be changed as appropriate without departing from the spirit of the present invention. On the other hand, not all the constituent elements shown in the above embodiment are necessarily essential, and can be appropriately selected. For example, when the combustion chamber expansion portion 50 is formed so as to spread outward in the radial direction outside the piston 20 when the piston 20 is at the top dead center, a turbulent flow is generated in the combustion chamber expansion portion 50. The squish part 45 is not essential.

DESCRIPTION OF SYMBOLS 1 Engine 2 Cylinder bore 3 Cylinder block 4 Cylinder head 6 Combustion chamber 20 Piston 27 Top surface 35 Top ring 45 Squish part 50 Combustion chamber expansion part A Cylinder axis D Depth of the combustion chamber expansion part 50

Claims (9)

A cylinder block formed with a cylinder bore;
A cylinder head coupled to one end surface of the cylinder block in the cylinder axial direction;
A piston that is reciprocally provided in the cylinder bore and that defines a combustion chamber between the cylinder head and the cylinder bore;
An internal combustion engine characterized in that at least one of the cylinder block and the cylinder head is formed with a combustion chamber expansion portion that expands the combustion chamber radially outward when the piston is at top dead center.   The internal combustion engine according to claim 1, wherein the combustion chamber expansion portion is formed so as to open at least at the one end surface of the cylinder block.   The combustion chamber extending portion is formed in the cylinder block with a depth that does not reach the top ring of the piston from the one end surface of the cylinder block when the piston is at top dead center. Item 3. The internal combustion engine according to Item 2. The combustion chamber has a squish portion that is a gap that causes squish when the piston reaches top dead center, and the squish portion includes a lower surface of the cylinder head and a top surface of the piston that extend in parallel to each other. Formed by
The internal combustion engine according to any one of claims 1 to 3, wherein the combustion chamber expansion portion is provided on a radially outer side of the squish portion.   The internal combustion engine according to any one of claims 1 to 4, wherein the combustion chamber expansion portion is formed at least on an intake side of the combustion chamber.   6. The combustion chamber expansion portion according to claim 1, wherein the combustion chamber expansion portion is formed only on the intake side of the combustion chamber or only at two locations on the intake side and exhaust side of the combustion chamber. The internal combustion engine described in 1.   The combustion chamber extending portion extends in a circumferential direction of the cylinder bore, and is formed so that a cross-sectional area becomes smaller toward a piston pin axial direction side of the piston. An internal combustion engine according to any one of the above.   The combustion chamber extending portion has a shape in which a radial width decreases from the one end surface to the other end of the cylinder block in a cross section along the radial direction of the cylinder bore. The internal combustion engine according to any one of claims 1 to 7.   The internal combustion engine according to any one of claims 1 to 8, wherein a contour of a radially outer side of the combustion chamber expansion portion has a waveform in a cylinder axial direction view.

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